Note: Descriptions are shown in the official language in which they were submitted.
~8~3~l,3
METHOD AND APPARATUS FOR THE AUTOMATED TESTING
OF VE~ICLE FUEL EVAPORATION CONTROL SYSTEMS
The present invention relates to a new and improved method for
conducting a test of a vehicle fuel evaporation control system and
an apparatus by which the methodology may be performed.
Background of the Invention
The testing of the functional systems of automobiles, trucks
and the like has progressed to the point that extremely
sophisticated and detailed tests may be performed to insure both
that the components of an au~omobile are working properly from a
mechanical and electro-mechanical point of view, and that system
performance is in accordance with mandated guidelines, whether they
- be on the federal, state or local level. The federal Environmental
Protection Administration ~EPA), for example, has promulgated
extensive regulations limiting the emissions of motor vehicles.
; Typically, a battery of tests may be performed by a test technician
; utilizing a computer-controlled interface and analysis system which
provides essentially real time evaluation of the parameters under
test.
One area in whi~h test technology has lagged, however, is in
the analysis of the system and components utilized to control fuel
evaporation to the atmosphere from the fuel tank and associated
piping. Such loss of fuel is both wasteful and environmentally
unsound, as the evaporated fuel, in addition to creating a possibly
;25 dangerous situation, contributes to unwanted hydrocarbon pollution.
Indeed, the EPA has imposed requirements that vehicle fuel
evaporation control systems be inspected for proper performance.
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Tyl ally, however, such inspections have been conducted manually,
without the benefit of automated test procedures which would
simplify the inspection and provide more reliable and consistent
testing.
It is accordingly a purpose of the present invention to
provide a method and apparatus for testing the integrity of the
fuel evaporation system on a vehicle.
Yet a further purpose of the present invention is to provide
such an apparatus and method which may be conducted in an
automated, non-intrusive manner.
Still a further purpose of the present invention is to provide
such a method and apparatus which may be incorporated into existing
test systems and test routines.
Still another purpose of the present invention is to provide
such a method and apparatus which can provide both qualitative and
quantitative measurements relating to performance of the fuel
evaporation control system.
Brief Description of the Invention
In accordance with the above and further purposes and
features, the method~logy of the present invention comprises the
charging of the fuel system with an appropriate non-reactive gas,
such as helium. In a preferred embodiment, charging of the system
is continued until the air of the fuel system is fully purged and
replaced with the inert gas. A test may then be performed to
confirm integrity of the control system evaporation collection
canister. The engine is then started, at which time other tests
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re ~ing to engine operation, typically automated, can be
performed. During the period of such testing, or independently if
desired, the vehicle exhaust is monitored for presence of the
charging gas.
In particular, the engine operating conditions, such as load,
speed and the like, may be varied during the monitoring process to
confirm proper operation of the canister purge valve. The presence
of the inert gas in the exhaust may be used to verify the integrity
of the lines in the fuel evaporation control system and that the
other components of the system operate properly. With use of a
quantitative measuring device at the exhaust, coupled with a
monitored injection of the gas, the amount of gas leaving the
system through the exhaust may be compared to that entering the
system. As the chosen gas is non-reactive, the difference in
~uantities reflect system losses such that a quantitative
measurement of such losses can be determined. Such analyses may
be performed concurrently with other automated emissions tests to
provide a fully automated and complete analysis of vehicle system
performance.
Hrief Description of~the Drawings
A fuller understanding of the present invention and its
specifications and features will be obtained upon consideration of
the following detailed description of a preferred, but nonetheless
illustrative embodiment of the invention when taken in conjunction
with the annexed Figures lA and B, which represent a schematic
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di~ -am of the apparatus for performing the present invention and
which further outline the process thereof.
Disclosure of the Invention
As shown in the Figures, the fuel evaporation system of a
typical automobile includes the fuel tank 10 of generally
conventional characteristics having a fuel inlet 12 capped by an
appropriate removable filler cap or stopper (not shown). AS
gasoline and other hydrocarbon fuels are volatile, the space above
the fuel in the gas tank 10 soon fills with fuel vapors, the extent
of which are dependent on the fuel, temperature, and ambient
pressure. As the temperature increases, for example, the extent
and rate of evaporation increases, increasing the partial pressure
of the evaporated fuel within the tank. To avoid excessive
pressure being developed, the filler cap is typically provided with
' 15 a pressure relief valve which allows the tank to be vented to the
atmosphere in the event the pressure within the tank exceeds a pre-
' set level. Such venting lowers the pressure to a safe level, but
i releases the fuel vapors directly to the atmosphere.
To limit such venting, in addition to a fuel line tnot shown)
which is adapted to withdraw fuel for combustion in the cylinders,the fuel tank 10 is provided with a second line 14, typically
located at the top of the tank, which leads to vapor collection
canister 16. The canister 16 is provided with an adsorbent 18,
typically activated charcoal, which adsorbs the fuel vapors. The
canister may be constructed with a perforated bottom or with
another venting means upon which the adsorbent rests which permits
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ai-~'as opposed to fuel vapors) from the gas tank to vent to the
atmosphere upon expansion and which further permits ambient air to
be drawn into ~he canister, as will be explained subsequently.
Egress of the fuel vapors through the open bottom, however, is
prevented by the carbon granules 18 with which the vapors come in
contact and are adsorbed upon within the canister. Thus, as
pressure within the tank rises, it is controlled by the venting of
fuel tank air to the atmosphere, while fuel vapors are prevented
from escape. Such action typically obviates operation of the
filler cap relief valve.
The canister 16 is connected to the engine air inlet line 22
by canister purge line 24, which is connected to the canister 16
typically through purge control valve 26. Valve 26 is typically
controlled by a vacuum source produced by operation of the engine,
such that valve 26 is not opened until the engine is running. The
valve may be further configured such that it opens at a specific
vacuum level corresponding to the engine attaining a pre-set speed.
Alternatively, the valve may be exclusively driven, controlled by
the vehicle's on-board computer system.
When the valve 26 opens, the pressure drop along air inlet 22
due to air flow to the engine is sufficient to draw the contents
of the canister through valve 26 and purge line 24 into the line
22 where it blends with the fresh air in the line. Fresh air may
be drawn into the canister 18 through its perforated bottom, mixing
with the adsorbed gas vapors, which are drawn out of the canister.
The blended gases in line 22 pass into the engine intake manifold
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28 ld are provided to the engine 38 for blending with fuel and
combustion. Exhausted gases from the combustion process are
collected in outlet or exhaust manifold 40, passed through
catalytic converter 42, and are then released to -the atmosphere
through tail pipe 44. In such a manner the gasoline vapors are
utilized, rather than being lost and vented to the atmosphere.
The present invention includes means to pressurize the fuel
system in a non-reactive, environmentally sound manner. Towards
that end, an appropriate gas, such as helium, is applied to the
fuel system in a manner to displace the air therein. Accordingly,
pressurized helium cylinder 28, having a pressure regulator 30 and
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.: a flow meter 32, is connected to the fuel filler line 12 by use of
.~ a cap 34 compatible with the cap lock located on the filler line
', to provide an air tight connection therewith. While the present
disclosure suggests the use of the noble gas helium as the charging
gas, it is to be recognized that other gases or combination of
~' gases may be utilized in place of helium, so long as they are non-
; ~ reactive with gasoline, are not adsorbed onto the carbon granules
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~ 18 in the canister 20, are non-reactive during combustion of the
'~J' ,''., 20 air fuel mixture in ~he engine cylinders, and are not affected by
passage through the catalytic converter 42. Such gases, for
' purposes of the present disclosure, shall be characterized as
' "inert". It is expected that at least other noble gases will be
appropriate for use in connection herewlth.
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The procedure of the present invention provides that thehelium is introduced into the fuel tank, wherein it blends with the
atmosphere therein and flows into the carbon canister 20. As the
canister purge control valve 26 is closed, the pressure being built
up in the fuel tank and associated piping by introduction of the
helium is vented through the perforated bottom 20 of the canister.
A detector 34 as know in the art may be placed proximate the
perforated bottom of the canister to detect the outflow of helium
and thus to confirm that the canister is properly connected to the
fuel system and is not blocked. Helium introduction can continue
for a sufficient period to fully purge the air from the fuel
system.
After canister integrity has been confirmed the automobile
engine may be started. At this time the test technician may
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perform other tests, such as engine and exhaust analysis, using
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known methods and technology.
With the engine started and running, purge control valve 26
opens, drawing the contents of the canister into the fuel line 22
and subsequently into the intake manifold 36 of the engine. The
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~; 20 pressure and flowrate of the helium source can be adjusted by
regulator 30 in conjunction with monitoring of the detector 34 to
assure that the flow of the contents of canister 18 to the engine
equals or exceeds the introduction of helium into the system such
that there is no longer any helium loss to the atmosphere through
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the bottom of the canister. It is to be recognized that the
monitoring of the detector 34, along with control of the flowrate
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f the helium, can be performed in an automated manner by the test
equipment using techniques well known in the art.
~ecause the helium or other chosen gas is inert and non-
reactive to the processes in the engine, it passes through intake
manifold 36, engine 38 and exhaust manifold 40, as well as
catalytic convertor 42, without change. Thus, the mass of helium
entering the system through filler line 12 equals the mass of
helium exiting through the tailpipe 44. Any loss of mass
represents leakage in the system, the extent of loss indicating the
magnitude Gf the leak.
~; Accordingly, the present invention may utilize a variety of
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sampling techniques, each of which may be conducted at the tailpipe
44. In a first embodiment, qualitative sampling means 46 as known
in the art are provided whereby the existence of helium in the
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exhaust verifies the integrity of the vapor lines in the fuel
'~'! evaporation control and confirms that the canister has undergone
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" purge. The timing of the first presence of helium in the exhaust
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as the speed of the engine is varied may be used to confirm that
~; purge valve 26 operates at the proper speed. In such tests only
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~ ~ 20 a portion of the exh~aust need be sampled.
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In a second embodiment, the entire exhaust, or a precisely-
determined portion thereof, may be captured by a volumetric
recovery means 48. The concentration of helium in the exhaust is
measured by quantitative analyzer 50, thus allowing the mass flow
; 25 of helium from the exhaust to be determined. This value is
compared with the helium flow into the fuel tank, providing a
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ql ltitative measure of the existence of leakage, if any.
Alternatively, with the engine running in a steady-state condition
whereby mass flow per unit time is constant, a controlled volume
sampled over a controlled time may be sampled and compared to input
flow over a corresponding time for leak analysis.
By the use of automated sampling detection and analysis
techniques as know to the art, the flow meter sampling system and
; measurement system, may all be interfaced to known engine
diagnostic systems and computers. This permits the sampling
process to be automated and performed concurrently with other tests
of the automobile.
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